1. Field of the Invention
This invention relates to a hose of impermeability and a process for manufacturing the same. More particularly, it relates to a hose having a very high level of fluid impermeability and satisfactory flexibility, strength and lightness in weight, and a process for manufacturing the same.
2. Description of the Related Art
Various kinds of rubber hoses have usually been used as, for example, fuel hoses in motor vehicles because of their ability to absorb vibration and their flexibility for assembly. They have, however, come to be replaced in recent years by hoses formed from resinous materials having a higher fuel impermeability than rubbers, since the fuel impermeability of hoses is important for environmental protection. Hoses formed from fluororesins have, among others, been preferred because of their particularly high fuel impermeability.
The fluororesins are, however, so expensive that it has been considered that they have to be used in the form of laminates with other materials that are less expensive. The formation of laminates requires special techniques, such as tetraetch treatment or plasma treatment, for the bonding of layers, and equipment therefor. The control on the permeation of fuel through the walls of hoses is expected to become still stricter, while it is also necessary to consider measures against the permeation of other fluids including carbon dioxide used as a refrigerant and hydrogen used in fuel cells. The hoses formed solely from organic materials, such as rubbers and resins including fluororesins, may not be able to satisfy the future requirement for fluid impermeability.
It has, therefore, been proposed that hoses have in their wall a barrier layer of a metal expected to have a very high fluid impermeability. For example, Japanese Patent Application Laid-Open No. 127101/1996 discloses a composite hose for hot or waste water having a wall formed of layers of polybutene, modified polyolefin and a metal. This hose is, however, designed for use in a building and does not, therefore, take into account any such factor as absorption of vibration, flexibility, gasoline resistance, or the resistance of its resin layers to hydrogen used in fuel cells. The hose of the type for which this invention is intended is, however, required to be capable of absorbing vibration, flexible for assembly, strong and light in weight, as well as having a high fluid impermeability.
Japanese Patent Application Laid-Open No. 275981/1995 discloses a resin-coated and corrugated hose made by coating a straight metal pipe with a resin layer, and corrugating the pipe and the resin layer by e.g. drawing or hydroforming. It also discloses a process for manufacturing such a hose. Although it intends to make a hose flexible and capable of absorbing vibration by corrugating it, the corrugation of a straight metal pipe and a resin layer covering it together has the drawback that the residual stress in the resin layer makes it difficult to retain the shape of the metal layer unless the metal layer has a relatively large thickness. The reason is that since up to about 20% of deformation is laminated tape wound about the resin layer; still in the range of elastic deformation for the resin, while it is already in the range of plastic deformation for the metal. In fact, the examples described therein show a metal layer thickness of 0.2 to 0.7 mm against a resin layer thickness of 0.5 to 1 mm. A metal layer having such a large thickness unavoidably adds to the cost of the hose and its weight and lowers its flexibility and its capability of absorbing vibration.